int set_grade( struct student *p, int n ){
	int cnt = 0;
	for (int i = 0;i<n;i++){
		if(p->score<60){
			cnt++;
		}if(p->score>=85){
			p->grade = 'A';
		}else if(p->score<85&&p->score>=70){
			p->grade = 'B';
		}else if(p->score>=60){
			p->grade = 'C';
			
		}else{
			p->grade = 'D';
		}p++
	}return cnt;
}
